1. Field
This application relates generally to semiconductor devices and to methods of making the devices.
2. Background of the Technology
A field-effect transistor (FET) is a type of transistor commonly used for weak-signal amplification (e.g., for amplifying wireless signals). The device can amplify analog or digital signals. It can also switch DC or function as an oscillator. In an FET, current flows along a semiconductor path called the channel. At one end of the channel, there is an electrode called the source. At the other end of the channel, there is an electrode called the drain. The physical diameter of the channel is fixed, but its effective electrical diameter can be varied by the application of a voltage to a control electrode called the gate. The conductivity of the FET depends, at any given instant in time, on the electrical diameter of the channel. A small change in gate voltage can cause a large variation in the current from the source to the drain. This is how the FET amplifies signals.
The gate of an FET can be a metal-semiconductor Schottky barrier (MESFET), a p-n junction (JFET), or a metal-oxide-semiconductor gate (MOSFET). The p-n junction FET (JFET) has a channel of N-type semiconductor (N-channel) or P-type semiconductor (P-channel) material and a gate of semiconductor material of the opposite semiconductor type on the channel. The Metal-Semiconductor-Field-Effect-Transistor (MESFET) has a channel of N-type or P-type semiconductor material and a Schottky metal gate on the channel.
Bipolar junction transistors (BJTs) are semiconductor devices having two back-to-back PN junctions. BJTs have a thin and typically lightly doped central region known as the base (B) having majority charge carriers of opposite polarity to those in the surrounding material. The two outer regions of the device are known as the emitter (E) and the collector (C). Under the proper operating conditions, the emitter injects majority charge carriers into the base region. Because the base is thin, most of these charge carriers will ultimately reach the collector. The emitter is typically highly doped to reduce resistance and the collector is typically lightly doped to reduce the junction capacitance of the collector-base junction.
Semiconductor devices such as FETs and BJTs are typically made using ion implantation techniques. Ion implantation, however, requires high temperature post implant anneals which increases the time required to manufacture the device and which can result in damage to the device.
Accordingly, there still exists a need for improved methods of making semiconductor devices such as FETs and BJTs which do not involve ion implantation.